What settings does Anti-spam Pro plugin have?

How does Anti-spam Pro plugin work?

Plugin distinguishes automatic and manually submitted comments and use different spam checks to block spam.

How does Anti-spam Pro plugin block automatic spam?

Anti-spam Pro plugin use few spam-bots characteristics to distinguish comments from automatic spam:

spam-bots does not use JavaScript

spam-bots are fully automatic and fills all the inputs using typical parsing patterns which can be easily trapped

Two extra hidden fields are added to comments form. First field should be filled with unique code. Second field should be empty.
If the user visits site, than first field is answered automatically with javascript, second field left blank and both fields are hidden by javascript and css and invisible for the user.
If the spammer will try to submit comment form, he will fail to fill code-input with correct code or will try to submit an empty field and spam comment will be automatically rejected.
The Anti-spam Pro input names have random unique suffix what adds extra layer of protection.

How does Anti-spam Pro plugin block manual spam?

Plugin uses "spam-points algorithm" to check if comment is spam.

Every comment will have +1 spam point for each truthy statement below:

URL field is not empty

comment contains too many links (3 or more by default; can be changed in Settings)

comment contains html

comment is too long (more than 2000 chars by default; can be changed in Settings)

Which license should be bought for Multi-site?

What about trackback spam?

Users rarely use trackbacks because it is manual and requires extra input. Spammers uses trackbacks because it is easy to cheat here.
Users use pingbacks very often because they work automatically. Spammers does not use pingbacks because backlinks are checked.
So trackbacks are blocked by default but pingbacks are enabled. You may enable trackbacks if you use it in [Settings] = [Anti-spam Pro] section.
You may read more about the difference between trackbacks and pingbacks.

Unobtrusive JavaScript

Anti-spam Pro plugin works with JavaScript disabled. JavaScript is disabled on less than 1% of devices.
Users with disabled JavaScript should manually copy-and-paste the code before submitting the comment.

And one more extra note...

If site has caching plugin enabled and cache is not cleared or if theme does not use 'comment_form' action
and there is no Ante-spam Pro plugin inputs in comments form -
Anti-spam Pro plugin tries to add hidden fields automatically using JavaScript.